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    SubjectRe: [PATCH] virtio-blk: Add stats VQ to collect information about devices
    On 08/17/2011 09:38 PM, Sasha Levin wrote:
    > On Wed, 2011-08-17 at 16:00 -0700, Avi Kivity wrote:
    > > On 08/16/2011 12:47 PM, Sasha Levin wrote:
    > > > This patch adds support for an optional stats vq that works similary to the
    > > > stats vq provided by virtio-balloon.
    > > >
    > > > The purpose of this change is to allow collection of statistics about working
    > > > virtio-blk devices to easily analyze performance without having to tap into
    > > > the guest.
    > > >
    > > >
    > >
    > > Why can't you get the same info from the host? i.e. read sectors?
    >
    > Some of the stats you can collect from the host, but some you can't.
    >
    > The ones you can't include all the timing statistics and the internal
    > queue statistics (read/write merges).

    Surely you can time the actual amount of time the I/O takes? It doesn't
    account for the virtio round-trip, but does it matter?

    Why is the merge count important for the host?

    >
    > The idea behind providing all of the stats on the stats vq (which is
    > basically what you see in '/dev/block/[device]/stats') is to give a
    > consistent snapshot of the state of the device.
    >
    >

    What can you do with it?

    --
    I have a truly marvellous patch that fixes the bug which this
    signature is too narrow to contain.



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